Khaled Bouamama | Universite Farehat Abes Setif (original) (raw)
Papers by Khaled Bouamama
High Pressure Research, 2005
ABSTRACT We report first-principles calculation results on the structural and elastic properties ... more ABSTRACT We report first-principles calculation results on the structural and elastic properties of ZnSxSe1−x alloy. The calculations done using density functional theory within the local density approximation and employing the virtual-crystal approximation. It is found that the lattice parameter, the phase transition pressure, and the elastic constants (and their derivative with respect to the pressure) follow a quadratic law in x.
Journal of the European Ceramic Society, 2007
Brillouin light scattering, Raman light scattering and visible-infrared reflectometry techniques ... more Brillouin light scattering, Raman light scattering and visible-infrared reflectometry techniques have been used to investigate, respectively, the elastic properties, the phonons and the optical properties of bulk textured polycrystalline yttrium-aluminum garnet doped with 2 at% neodymium obtained by the sintering of commercial oxides. From the analysis of the observed bulk longitudinal and transverse acoustic modes with the knowledge of the refractive index 1.81 inferred from the visible reflectometry, the two independent effective elastic constants of the isotropic polycrystal C 11 = 362 GPa and (C 11 − C 12 )/2 = 121 GPa are determined leading to the value of the bulk modulus B = (C 11 + 2C 12 )/3 = 200 GPa. The ratio ε 0 /ε ∞ = 3.1 and the optic permittivity ε ∞ = 3.46 are derived from the infrared reflectivity data. Pair potential calculations of the three single crystal elastic constants c 11 = 340, c 12 = 127 and c 44 = 112 GPa, of the bulk modulus B = (c 11 + 2c 12 )/3 = 198 GPa, of the zone-center ( ) phonons and of the permittivity function provide good comparison with our experimental results. (P. Djemia). there are two different sites for Al ions: namely, octahedral 16 (a) and tetrahedral 24 (d) in the lattice.
Journal of the European Ceramic Society, 2007
Brillouin light scattering, Raman light scattering and visible-infrared reflectometry techniques ... more Brillouin light scattering, Raman light scattering and visible-infrared reflectometry techniques have been used to investigate, respectively, the elastic properties, the phonons and the optical properties of bulk textured polycrystalline yttrium-aluminum garnet doped with 2 at% neodymium obtained by the sintering of commercial oxides. From the analysis of the observed bulk longitudinal and transverse acoustic modes with the knowledge of the refractive index 1.81 inferred from the visible reflectometry, the two independent effective elastic constants of the isotropic polycrystal C 11 = 362 GPa and (C 11 − C 12 )/2 = 121 GPa are determined leading to the value of the bulk modulus B = (C 11 + 2C 12 )/3 = 200 GPa. The ratio ε 0 /ε ∞ = 3.1 and the optic permittivity ε ∞ = 3.46 are derived from the infrared reflectivity data. Pair potential calculations of the three single crystal elastic constants c 11 = 340, c 12 = 127 and c 44 = 112 GPa, of the bulk modulus B = (c 11 + 2c 12 )/3 = 198 GPa, of the zone-center ( ) phonons and of the permittivity function provide good comparison with our experimental results. (P. Djemia). there are two different sites for Al ions: namely, octahedral 16 (a) and tetrahedral 24 (d) in the lattice.
Computational Materials Science, 2009
The lattice dynamics and elastic properties of the ternary AgBr 1Àx Cl x alloy have been studied ... more The lattice dynamics and elastic properties of the ternary AgBr 1Àx Cl x alloy have been studied using firstprinciples calculations. These are done using the density-functional perturbation theory (DFPT) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (x TO and x LO ) and of the acoustical phonon frequencies (x TA and x LA ), the high-frequency dielectric coefficient (e 1 ), the dynamic effective charge (Z * ) and the elastic constants (C 11 , C 12 , C 44 )a sa function of the composition (x). We find that the phonon frequencies as well as the elastic constants follow a quadratic law in x and agree well with the available experimental results. The elastic constant tensors for simple cubic 8-atom supercells with x = 0.25, 0.5 and 0.75 have been computed and are in good agreement with those obtained from VCA and experiments.
High Pressure Research, 2007
ABSTRACT High-pressure effects on the lattice dynamics and dielectric properties of the BN, BP, B... more ABSTRACT High-pressure effects on the lattice dynamics and dielectric properties of the BN, BP, BAs, BSb and BBi alloys have been carried out using the density-functional perturbation theory within the local density approximation. We study the variation of the optical phonon frequencies (ωTO and ωLO), the high-frequency dielectric coefficient (ε∞) and the dynamic effective charge (Z*) with pressure. The ωTO and ωLO have a quadratic form with pressure for all boron compounds. The obtained ε∞ and Z* for BN, BP remain constant with pressure. However, for BAs, BSb and BBi, ε∞ and Z* have a quadratic form with pressure. Our results are in good agreement with the available experimental data for BN and BP and they allow prediction for BAs, BSb and BBi.
Modern Physics Letters B, 2009
ABSTRACT The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first-princ... more ABSTRACT The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first-principles calculations. These are done using the density-functional perturbation theory (DFPT) within the local density approximation (LDA) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (ωTO and ωLO), the high-frequency dielectric coefficient (ε∞) and the dynamic effective charge (Z*) as a function of the composition (x). We found that the ωTO and ωLO follow a quadratic law in x and agree well with the experiment which proves that the VCA is a reliable method for mixed modes determination (2 bonds-1 mode). The obtained ε∞ and Z* have a quadratic form with x. We have also predicted the behavior of the optical and acoustical phonons with x at the high symmetry point X and L.
High Pressure Research, 2007
High-pressure effects on the lattice dynamics and dielectric properties of the BN, BP, BAs, BSb a... more High-pressure effects on the lattice dynamics and dielectric properties of the BN, BP, BAs, BSb and BBi alloys have been carried out using the density-functional perturbation theory within the local density approximation. We study the variation of the optical phonon frequencies (ω TO and ω LO ), the high-frequency dielectric coefficient ( ∞ ) and the dynamic effective charge (Z * ) with pressure. The ω TO and ω LO have a quadratic form with pressure for all boron compounds. The obtained ∞ and Z * for BN, BP remain constant with pressure. However, for BAs, BSb and BBi, ∞ and Z * have a quadratic form with pressure. Our results are in good agreement with the available experimental data for BN and BP and they allow prediction for BAs, BSb and BBi.
Modern Physics Letters B, 2009
ABSTRACT The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first-princ... more ABSTRACT The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first-principles calculations. These are done using the density-functional perturbation theory (DFPT) within the local density approximation (LDA) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (ωTO and ωLO), the high-frequency dielectric coefficient (ε∞) and the dynamic effective charge (Z*) as a function of the composition (x). We found that the ωTO and ωLO follow a quadratic law in x and agree well with the experiment which proves that the VCA is a reliable method for mixed modes determination (2 bonds-1 mode). The obtained ε∞ and Z* have a quadratic form with x. We have also predicted the behavior of the optical and acoustical phonons with x at the high symmetry point X and L.
Journal of Physics: Conference Series, 2013
Residual defects after growth of semiconductors crystals is a hot issue to be solved for manufact... more Residual defects after growth of semiconductors crystals is a hot issue to be solved for manufacturing new efficient electronic or optic devices. These defects can be conveniently observed using birefringence optical microscopy for extended defects that will create a local strain field which in turn can cause a nominally isotropic optical material to become anisotropic and induce birefringence. In order to perform a quantitative analysis, the knowledge of the photoelastic constants (P ij ) of the material that measure the strength of the change of the refractive index under application of strains or stresses is necessary. As an experimental determination of the whole set of constants is not always possible, a theoretical evaluation can be of valuable interest. In this work, we propose ab-initio calculations by the WIEN2k program of the optical properties of the zinc blende silicon carbide polytype with a self-consistent scheme by solving the Kohn-Sham equations using a full potential linearized augmented plane waves (FPLAPW) method in the framework of the density functional theory (DFT) along with the generalized gradient approximation (GGA) pseudo-potentials. A combination of specific compressive and tensile strains is applied to the two atoms unit cell and the tensor containing each specific combination of the P ij constants is extracted.
Journal of the European Ceramic Society, 2007
Brillouin light scattering, Raman light scattering and visible-infrared reflectometry techniques ... more Brillouin light scattering, Raman light scattering and visible-infrared reflectometry techniques have been used to investigate, respectively, the elastic properties, the phonons and the optical properties of bulk textured polycrystalline yttrium-aluminum garnet doped with 2 at% neodymium obtained by the sintering of commercial oxides. From the analysis of the observed bulk longitudinal and transverse acoustic modes with the knowledge of the refractive index 1.81 inferred from the visible reflectometry, the two independent effective elastic constants of the isotropic polycrystal C 11 = 362 GPa and (C 11 − C 12 )/2 = 121 GPa are determined leading to the value of the bulk modulus B = (C 11 + 2C 12 )/3 = 200 GPa. The ratio ε 0 /ε ∞ = 3.1 and the optic permittivity ε ∞ = 3.46 are derived from the infrared reflectivity data. Pair potential calculations of the three single crystal elastic constants c 11 = 340, c 12 = 127 and c 44 = 112 GPa, of the bulk modulus B = (c 11 + 2c 12 )/3 = 198 GPa, of the zone-center ( ) phonons and of the permittivity function provide good comparison with our experimental results. (P. Djemia). there are two different sites for Al ions: namely, octahedral 16 (a) and tetrahedral 24 (d) in the lattice.
Journal of Alloys and Compounds, 2012
First-principles pseudopotential calculations of the lattice constants and of the single-crystal ... more First-principles pseudopotential calculations of the lattice constants and of the single-crystal elastic constants of Ti 1−x Zr x N (0 ≤ x ≤ 1) alloys were carried out. These calculations were performed using density functional perturbation theory (DFPT) within the virtual crystal approximation (VCA) for the disordered alloys and the supercell method (SC) for the ordered alloys. For the exchange-correlation potential we used both the local density (LDA) and the generalized gradient methods (GGA). The calculated equilibrium lattice parameters exhibit a positive deviation from Vegard's rule corresponding to a positive bowing parameter, while the calculated single-crystal stiffnesses, namely C 11 , C 12 and C 44 , gradually decrease from TiN to ZrN. In a second stage, in the frame of anisotropic elasticity, we have estimated by homogenization methods the averaged stiffnesses C ij , direction dependent Young's moduli and Poisson's ratios of polycrystalline Ti 1−x Zr x N (0 ≤ x ≤ 1) alloys considering a {1 1 1}-fiber texture.
First-principles pseudopotential calculations of the lattice constants and of the single-crystal ... more First-principles pseudopotential calculations of the lattice constants and of the single-crystal elastic constants for Ti x Ta 1 −x N (0≤ x ≤ 1) alloys with B1-rocksalt structure were first carried out. These calculations were performed using density functional perturbation theory (DFPT) within the virtual crystal approximation (VCA) for the disordered alloys and the supercell method (SC) for the ordered alloys, with the ABINIT program. For disordered structures, partial comparisons of the lattice constants and of the bulk modulus are provided with calculations that used the coherent potential approximation (CPA) with the exact muffin-tin orbitals (EMTO). For the exchange-correlation potential we used the generalized gradient methods (GGA). The calculated equilibrium lattice parameters by VCA are in good agreement with the stress-free lattice parameters a 0 and exhibit a positive deviation from Vegard's rule corresponding to a positive bowing parameter while the calculated single-crystal stiffness c 12 and c 44 , gradually increase when c 11 decreases from TaN to TiN. In a second stage, we have estimated by homogenization methods the averaged stiffnesses bc ij >, the Young modulus and Poisson ratio of polycrystalline Ti x Ta 1 − x N (0≤ x ≤ 1) alloys considering a random orientation of crystallites. Finally, comparisons are made with the experimental effective out-of-plane shear elastic modulus C 44 and the effective out-of-plane longitudinal elastic constant C 33 measured by Brillouin light scattering and picosecond ultrasonics, respectively, on thin films elaborated by magnetron sputtering.
High Pressure Research, 2005
ABSTRACT We report first-principles calculation results on the structural and elastic properties ... more ABSTRACT We report first-principles calculation results on the structural and elastic properties of ZnSxSe1−x alloy. The calculations done using density functional theory within the local density approximation and employing the virtual-crystal approximation. It is found that the lattice parameter, the phase transition pressure, and the elastic constants (and their derivative with respect to the pressure) follow a quadratic law in x.
Journal of the European Ceramic Society, 2007
Brillouin light scattering, Raman light scattering and visible-infrared reflectometry techniques ... more Brillouin light scattering, Raman light scattering and visible-infrared reflectometry techniques have been used to investigate, respectively, the elastic properties, the phonons and the optical properties of bulk textured polycrystalline yttrium-aluminum garnet doped with 2 at% neodymium obtained by the sintering of commercial oxides. From the analysis of the observed bulk longitudinal and transverse acoustic modes with the knowledge of the refractive index 1.81 inferred from the visible reflectometry, the two independent effective elastic constants of the isotropic polycrystal C 11 = 362 GPa and (C 11 − C 12 )/2 = 121 GPa are determined leading to the value of the bulk modulus B = (C 11 + 2C 12 )/3 = 200 GPa. The ratio ε 0 /ε ∞ = 3.1 and the optic permittivity ε ∞ = 3.46 are derived from the infrared reflectivity data. Pair potential calculations of the three single crystal elastic constants c 11 = 340, c 12 = 127 and c 44 = 112 GPa, of the bulk modulus B = (c 11 + 2c 12 )/3 = 198 GPa, of the zone-center ( ) phonons and of the permittivity function provide good comparison with our experimental results. (P. Djemia). there are two different sites for Al ions: namely, octahedral 16 (a) and tetrahedral 24 (d) in the lattice.
Journal of the European Ceramic Society, 2007
Brillouin light scattering, Raman light scattering and visible-infrared reflectometry techniques ... more Brillouin light scattering, Raman light scattering and visible-infrared reflectometry techniques have been used to investigate, respectively, the elastic properties, the phonons and the optical properties of bulk textured polycrystalline yttrium-aluminum garnet doped with 2 at% neodymium obtained by the sintering of commercial oxides. From the analysis of the observed bulk longitudinal and transverse acoustic modes with the knowledge of the refractive index 1.81 inferred from the visible reflectometry, the two independent effective elastic constants of the isotropic polycrystal C 11 = 362 GPa and (C 11 − C 12 )/2 = 121 GPa are determined leading to the value of the bulk modulus B = (C 11 + 2C 12 )/3 = 200 GPa. The ratio ε 0 /ε ∞ = 3.1 and the optic permittivity ε ∞ = 3.46 are derived from the infrared reflectivity data. Pair potential calculations of the three single crystal elastic constants c 11 = 340, c 12 = 127 and c 44 = 112 GPa, of the bulk modulus B = (c 11 + 2c 12 )/3 = 198 GPa, of the zone-center ( ) phonons and of the permittivity function provide good comparison with our experimental results. (P. Djemia). there are two different sites for Al ions: namely, octahedral 16 (a) and tetrahedral 24 (d) in the lattice.
Computational Materials Science, 2009
The lattice dynamics and elastic properties of the ternary AgBr 1Àx Cl x alloy have been studied ... more The lattice dynamics and elastic properties of the ternary AgBr 1Àx Cl x alloy have been studied using firstprinciples calculations. These are done using the density-functional perturbation theory (DFPT) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (x TO and x LO ) and of the acoustical phonon frequencies (x TA and x LA ), the high-frequency dielectric coefficient (e 1 ), the dynamic effective charge (Z * ) and the elastic constants (C 11 , C 12 , C 44 )a sa function of the composition (x). We find that the phonon frequencies as well as the elastic constants follow a quadratic law in x and agree well with the available experimental results. The elastic constant tensors for simple cubic 8-atom supercells with x = 0.25, 0.5 and 0.75 have been computed and are in good agreement with those obtained from VCA and experiments.
High Pressure Research, 2007
ABSTRACT High-pressure effects on the lattice dynamics and dielectric properties of the BN, BP, B... more ABSTRACT High-pressure effects on the lattice dynamics and dielectric properties of the BN, BP, BAs, BSb and BBi alloys have been carried out using the density-functional perturbation theory within the local density approximation. We study the variation of the optical phonon frequencies (ωTO and ωLO), the high-frequency dielectric coefficient (ε∞) and the dynamic effective charge (Z*) with pressure. The ωTO and ωLO have a quadratic form with pressure for all boron compounds. The obtained ε∞ and Z* for BN, BP remain constant with pressure. However, for BAs, BSb and BBi, ε∞ and Z* have a quadratic form with pressure. Our results are in good agreement with the available experimental data for BN and BP and they allow prediction for BAs, BSb and BBi.
Modern Physics Letters B, 2009
ABSTRACT The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first-princ... more ABSTRACT The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first-principles calculations. These are done using the density-functional perturbation theory (DFPT) within the local density approximation (LDA) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (ωTO and ωLO), the high-frequency dielectric coefficient (ε∞) and the dynamic effective charge (Z*) as a function of the composition (x). We found that the ωTO and ωLO follow a quadratic law in x and agree well with the experiment which proves that the VCA is a reliable method for mixed modes determination (2 bonds-1 mode). The obtained ε∞ and Z* have a quadratic form with x. We have also predicted the behavior of the optical and acoustical phonons with x at the high symmetry point X and L.
High Pressure Research, 2007
High-pressure effects on the lattice dynamics and dielectric properties of the BN, BP, BAs, BSb a... more High-pressure effects on the lattice dynamics and dielectric properties of the BN, BP, BAs, BSb and BBi alloys have been carried out using the density-functional perturbation theory within the local density approximation. We study the variation of the optical phonon frequencies (ω TO and ω LO ), the high-frequency dielectric coefficient ( ∞ ) and the dynamic effective charge (Z * ) with pressure. The ω TO and ω LO have a quadratic form with pressure for all boron compounds. The obtained ∞ and Z * for BN, BP remain constant with pressure. However, for BAs, BSb and BBi, ∞ and Z * have a quadratic form with pressure. Our results are in good agreement with the available experimental data for BN and BP and they allow prediction for BAs, BSb and BBi.
Modern Physics Letters B, 2009
ABSTRACT The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first-princ... more ABSTRACT The lattice dynamics of the ternary ZnSe1-xTex alloy have been studied using first-principles calculations. These are done using the density-functional perturbation theory (DFPT) within the local density approximation (LDA) and employing the virtual-crystal approximation (VCA). We study the variation of the optical phonon frequencies (ωTO and ωLO), the high-frequency dielectric coefficient (ε∞) and the dynamic effective charge (Z*) as a function of the composition (x). We found that the ωTO and ωLO follow a quadratic law in x and agree well with the experiment which proves that the VCA is a reliable method for mixed modes determination (2 bonds-1 mode). The obtained ε∞ and Z* have a quadratic form with x. We have also predicted the behavior of the optical and acoustical phonons with x at the high symmetry point X and L.
Journal of Physics: Conference Series, 2013
Residual defects after growth of semiconductors crystals is a hot issue to be solved for manufact... more Residual defects after growth of semiconductors crystals is a hot issue to be solved for manufacturing new efficient electronic or optic devices. These defects can be conveniently observed using birefringence optical microscopy for extended defects that will create a local strain field which in turn can cause a nominally isotropic optical material to become anisotropic and induce birefringence. In order to perform a quantitative analysis, the knowledge of the photoelastic constants (P ij ) of the material that measure the strength of the change of the refractive index under application of strains or stresses is necessary. As an experimental determination of the whole set of constants is not always possible, a theoretical evaluation can be of valuable interest. In this work, we propose ab-initio calculations by the WIEN2k program of the optical properties of the zinc blende silicon carbide polytype with a self-consistent scheme by solving the Kohn-Sham equations using a full potential linearized augmented plane waves (FPLAPW) method in the framework of the density functional theory (DFT) along with the generalized gradient approximation (GGA) pseudo-potentials. A combination of specific compressive and tensile strains is applied to the two atoms unit cell and the tensor containing each specific combination of the P ij constants is extracted.
Journal of the European Ceramic Society, 2007
Brillouin light scattering, Raman light scattering and visible-infrared reflectometry techniques ... more Brillouin light scattering, Raman light scattering and visible-infrared reflectometry techniques have been used to investigate, respectively, the elastic properties, the phonons and the optical properties of bulk textured polycrystalline yttrium-aluminum garnet doped with 2 at% neodymium obtained by the sintering of commercial oxides. From the analysis of the observed bulk longitudinal and transverse acoustic modes with the knowledge of the refractive index 1.81 inferred from the visible reflectometry, the two independent effective elastic constants of the isotropic polycrystal C 11 = 362 GPa and (C 11 − C 12 )/2 = 121 GPa are determined leading to the value of the bulk modulus B = (C 11 + 2C 12 )/3 = 200 GPa. The ratio ε 0 /ε ∞ = 3.1 and the optic permittivity ε ∞ = 3.46 are derived from the infrared reflectivity data. Pair potential calculations of the three single crystal elastic constants c 11 = 340, c 12 = 127 and c 44 = 112 GPa, of the bulk modulus B = (c 11 + 2c 12 )/3 = 198 GPa, of the zone-center ( ) phonons and of the permittivity function provide good comparison with our experimental results. (P. Djemia). there are two different sites for Al ions: namely, octahedral 16 (a) and tetrahedral 24 (d) in the lattice.
Journal of Alloys and Compounds, 2012
First-principles pseudopotential calculations of the lattice constants and of the single-crystal ... more First-principles pseudopotential calculations of the lattice constants and of the single-crystal elastic constants of Ti 1−x Zr x N (0 ≤ x ≤ 1) alloys were carried out. These calculations were performed using density functional perturbation theory (DFPT) within the virtual crystal approximation (VCA) for the disordered alloys and the supercell method (SC) for the ordered alloys. For the exchange-correlation potential we used both the local density (LDA) and the generalized gradient methods (GGA). The calculated equilibrium lattice parameters exhibit a positive deviation from Vegard's rule corresponding to a positive bowing parameter, while the calculated single-crystal stiffnesses, namely C 11 , C 12 and C 44 , gradually decrease from TiN to ZrN. In a second stage, in the frame of anisotropic elasticity, we have estimated by homogenization methods the averaged stiffnesses C ij , direction dependent Young's moduli and Poisson's ratios of polycrystalline Ti 1−x Zr x N (0 ≤ x ≤ 1) alloys considering a {1 1 1}-fiber texture.
First-principles pseudopotential calculations of the lattice constants and of the single-crystal ... more First-principles pseudopotential calculations of the lattice constants and of the single-crystal elastic constants for Ti x Ta 1 −x N (0≤ x ≤ 1) alloys with B1-rocksalt structure were first carried out. These calculations were performed using density functional perturbation theory (DFPT) within the virtual crystal approximation (VCA) for the disordered alloys and the supercell method (SC) for the ordered alloys, with the ABINIT program. For disordered structures, partial comparisons of the lattice constants and of the bulk modulus are provided with calculations that used the coherent potential approximation (CPA) with the exact muffin-tin orbitals (EMTO). For the exchange-correlation potential we used the generalized gradient methods (GGA). The calculated equilibrium lattice parameters by VCA are in good agreement with the stress-free lattice parameters a 0 and exhibit a positive deviation from Vegard's rule corresponding to a positive bowing parameter while the calculated single-crystal stiffness c 12 and c 44 , gradually increase when c 11 decreases from TaN to TiN. In a second stage, we have estimated by homogenization methods the averaged stiffnesses bc ij >, the Young modulus and Poisson ratio of polycrystalline Ti x Ta 1 − x N (0≤ x ≤ 1) alloys considering a random orientation of crystallites. Finally, comparisons are made with the experimental effective out-of-plane shear elastic modulus C 44 and the effective out-of-plane longitudinal elastic constant C 33 measured by Brillouin light scattering and picosecond ultrasonics, respectively, on thin films elaborated by magnetron sputtering.